Spherical d12 with an icosahedron-shaped hollow inside and a ball rolling around in it, so it should land with a number upward.
Added some extra pieces to hold the centers of the 4, 6, 8, 9, 0 in place.
Print was okay, though the centers of the 8 fell out. Doesn't quite always land face-up, still working on it.
Might be cool in Frosted Detail, with the transparency and the liquid support material.